1. Field of the Invention
The invention relates to a clip for a fuse-holder and to a fuse-holder equipped with at least one such clip.
2. Description of the Related Art
In the domain of the protection of electrical installations, it is known to use so-called cylindrical fuse cartridges, i.e. of which the two terminals or cartridges are cylindrical, these terminals or cartridges being provided to be received in clips, themselves connected to electrical lines. The clips of the known devices comprise rounded parts provided to substantially follow the shape of a part of the circumference of the cylindrical cartridge of a fuse. There is thus surface contact between the clips and the cartridge.
Furthermore, in order to withstand an effort of repulsion created in the event of an overintensity, between the cartridge of a fuse and the clip in which it is received, the standards provide that the force of abutment or of pressure of a clip on a fuse cartridge must be of the order of several tens of Newton. For example, in the case of a fuse of which the terminals have a diameter of 27 mm, the force of abutment must be greater than or equal to 45 Newton. Although such a force is useful when the fuse is in place in the clip, it opposes the positioning and extraction of the fuse in and from the clip, with the result that the efforts that an operator must exert on these occasions are intense, to the point of generating false manoeuvres. In this way, it is not rare that, when a fuse is extracted from a known clip, the effort to be exerted, which must overcome the frictions generated at the level of the contact surfaces, is so great that it induces a violent tearing of the fuse which xe2x80x9cjumpsxe2x80x9d from its housing in the fuse-holder and drops onto the floor.
In addition, in the known devices, the contacts between the cylindrical cartridge of a fuse and the two lugs of a clip may be concentrated in two zones distributed on either side of the cartridge, with the result that the dimensioning of the clips must be provided, considering the fact that the breakdown current is divided into two at the level of each clip. This imposes the constitution of thick, therefore rigid, clips, and induces additional difficulties when a fuse is being positioned or extracted.
In the devices of the prior art, it is common to place a plurality of fuses in parallel, a trigger circuit being provided for this purpose. Taking into account the considerable forces which must be exerted on the fuse during installation or removal, the trigger circuit must be able to withstand a very considerable force which leads to it being overdimensioned, this increasing the cost of a fuse-holder.
It is a more particular object of the invention to overcome these drawbacks by proposing a clip of the afore-mentioned type in which a fuse cartridge of circular cross-section is efficiently held and which allows easy introduction and extraction of such a cartridge.
In this spirit, the invention relates to a clip for fuse-holder comprising two lugs designed to define between them a space for receiving a fuse cartridge with circular cross-section, characterized in that said lugs are folded in directions parallel to a central axis of the cartridge set in the clip such that they each form two electrical contact and mechanical support lines on the radial surface of this cartridge, these two lines being globally parallel to this axis.
Thanks to the invention, the contact between each of the lugs of the clip and the cartridge of a fuse is exerted along two lines, with the result that the efforts of friction which must be overcome when a fuse is being positioned or extracted, are generated solely between these lines and the outer radial surface of the cartridge. They are therefore less than in the case of surface contacts as obtained with the devices of the state of the art. Once the cartridge is in place in the clip, the latter is efficiently maintained thanks to the cooperation of the four lines of contact formed by the two clips. These four lines of contact also result in a division into four of the breakdown current, and even into three in the case of geometrical imperfection resulting in an abutment of the cartridge on three of the four lines of contact formed by the two clips. The maximum current transiting in each of the zones of contact is thus equal to a quarter or a third of the breakdown current of the fuse, which makes it possible electrically to dimension the clips as a function of this value, and not as a function of half the breakdown current as in the devices of the state of the art. The invention also makes it possible appropriately to dimension the trigger circuits provided for the combined manoeuvre of a plurality of fuses, since the efforts that they must withstand are substantially less than in the devices of the state of the art.
According to advantageous aspects of the invention, the clip incorporates one or more of the following characteristics:
The traces of the two electrical contact and mechanical support lines in a plane perpendicular to the radial surface of the cartridge are included in a sector, centred on the trace of this central axis in this plane, of apex angle smaller than 30xc2x0. In particular, this apex angle may be provided to be included between 20 and 28xc2x0, preferably of the order of 24xc2x0. Thanks to this construction, the two electrical contact and mechanical support lines formed on each lug are relatively close to one another and the line character of the contact may be guaranteed insofar as the outer radial surface of the cartridge cannot penetrate between these lines to the point of generating a surface contact.
Each lug comprises, between the lines of contact, a zone deformed outwardly with respect to a principal plane of the lug. This construction makes it possible to produce the two lines of contact in particularly simple manner. The deformed zone advantageously comprises two surfaces inclined with respect to the principal plane of each lug and with respect to one another. In that case, the apex angle of this deformed zone, which is defined by the two inclined surfaces, is advantageously included between 80 and 100xc2x0, preferably of the order of 90xc2x0.
The ends of the lugs are divergent with respect to a median axis of the clip. The angle of divergence of these ends may be provided to be included between 16 and 24xc2x0, preferably of the order of 20xc2x0. Thanks to this arrangement, the ends of the lugs form a cone for slide during introduction of the cartridge of the fuse in the clip, hence a progressivity of the effort that the operator must exert for positioning the cartridge, such progressivity being felt by the user as an additional comfort. Moreover, the flared ends assist the movement of extraction of the fuse cartridge as they exert on the cartridge an elastic effort of ejection with respect to the clip. The lugs of the clip of the invention thus work both in flexion and in friction during the movements of positioning and of extraction of the fuse.
An outer holding spring is provided in abutment on the lugs of the clip at the level of the outwardly deformed zones, with respect to a principal plane of each lug, these zones being defined between the lines of contact. This outer spring ensures the effort of axial clamping of the fuse cartridge when the latter is in place in the clip.
The invention also relates to a fuse-holder equipped with at least one clip as described hereinabove. Such a fuse-holder is easier to manipulate, while remaining reliable and of moderate cost.